The present invention relates to novel diaminoarylsulfones corresponding to formula (I) ##STR2## wherein R.sub.1, R.sub.2, and R.sub.3 are independently C.sub.1 -C.sub.12 alkyl. The present invention also relates to a process for the preparation of these new compounds and to their use.
Aromatic diamines play an important role in the production of polyurethane elastomers, enabling the use of tolylene diisocyanate ("TDI") prepolymers, which have a good storage stability and a suitable viscosity for casting.
The technically most important diamine is 3,3'-dichloro-4,4'-diaminodiphenylmethane ("MOCA") but it has certain disadvantages. Extensive efforts to find substitutes have therefore been made, and numerous products which can be reacted with TDI prepolymers to produce elastomers have subsequently become known. See, e.g., C. Hepburn, Polyurethane Elastomers, Applied Science Publishers Ltd., London, N.Y. (1982), pages 101 to 138.
Among these products, however, only 3,5-diamino-4-chlorobenzoic acid isobutyl ester (described in German Auslegeschrift 1,803,635) has achieved any practical importance. Like all the known slowly reacting diamines which give rise to high quality products, this compound has a symmetrical structure. This ester diamine combines excellent processing properties with a high level of quality in the elastomers obtained from it. Disadvantages of this compound include its relatively expensive method of preparation and, especially, the safety measures which are required for dinitration.
It has now surprisingly been found that the diaminoarylsulfones according to the present invention are well suited for use as diamine chain extending agents for the preparation of elastomers, especially when using the casting process. This suitability applies particularly to 1,3-diamino-2,4-dimethyl-5-methylsulfonylbenzene.
In DE-OS 2,001,772 and DE-OS 2,025,896 it has already been proposed to use 3,5-diamino-1-ethyl-sulfonyl-4-chlorobenzene as chain extender for the preparation of polyurethane ("PUR") elastomers. Halogenated sulfones of this type have, however, one serious disadvantage, both by comparison with the analogously structured halogenated benzoic acid esters and by comparison with the compounds according to this invention, in that they are very slow to react. Even at elevated temperatures, the residence time required in the mold is several hours. Moreover, the mechanical properties are only average, despite the symmetrical structure of the compound.
It must therefore be regarded as all the more surprising in the light of this state of the art that the sulfones according to the invention, which are asymmetric and free from chlorine atoms, not only provide advantageous processing properties and rapid hardening but also give rise to products with excellent mechanical properties.
The diaminoarylsulfones according to the invention result in PUR elastomers which have properties equal to those of the products according to DE-AS 1,803,635 but have the added advantages of being easier to prepare and, in particular, of requiring no special safety measures for the dinitration stage. The reactivity is somewhat higher than that of the above mentioned ester diamine, an advantage for a mechanical casting process and for the use of the product in the RIM process.